U.S. Pat. No. 4,044,521 discloses extruded plastic support members each having a hook portion for mounting on a flange portion of a purlin and a planar support portion for holding up an edge portion of a roof liner panel. Fibrous insulation batts may be installed above the panels between the purlins. The system is adapted only for flat or nearly flat roofs and only for new construction, wherein the insulation batts are installed from above as the exterior roof panel installation progresses.